Dear Tim,
Let me ask you a question-does your Uke hit the ground each time you do shiho nage?If the answer is yes, why do you need to have to throw with power?Is it not enough to simply make sure uke hits the deck? When I trained with Sekiya Sensei[ Chiba Sensei' father in law] he never at any time used powerful waza.At the same time he always pinned or threw you with ease-totally painless and safe.
Shiho nage done incorrectly with power can dislocate the collar bone and also plays havoc with the elbow joints.
Rather than try to be Rambo or King Kong,why not forsake power and acquire skills?If you receive /use power its unlikely your or your ukes body will be fit after 30 /40 years training.
your throwing direction imo is not qite right.Ask yourself the question , do you want to send uke to the floor or throw uke up in the air and thiry feet away [for example]??I would suggest you should send uke to the floor in the shortest route possible ie to the ground [downward to the mat ].
Have a nice day , Joe.

Just to echo what Mr. Curran here is saying, sure, you can fairly easily perform a powerfully nasty shihonage, especially on an unsuspecting (read that untrained) person. That said, spending the time and sweat equity to learn to do it smoothly, softly ending with a proper pin is a higher level skill that (at least IMHO) will serve you well. Even after a whole lot of years I find it to be a challenging thing to accomplish, especially with injuries and some congenital problems physically. That said, at this point doing it in a mean and nasty way ain't all that difficult. If you can do it in the way Mr. Curran has described, you always have the option to make it quite devastating. That option is always there if you need it a and get there from the right direction, so to speak. But if all you have is the mean, nasty, bust stuff up version, there are times you might find that you have no other options but mean, nasty, and bust stuff up. I'd rather have more options...

FWIW I've had my share of injuries from overly ambitious shihonage being applied to me. Frankly, these days, I'll bow out of training with anyone I don't already know. The body just can't take the enthusiasm any longer...

But all that said... Lots of opinions and ideas on these topics... All have their merits depending on what you're looking for.